The present invention relates to power supply scheme for a plurality of fans used to cool an electronic chassis, and in particular, to an apparatus and method of providing redundant power and redundant fan speed control to a plurality of fans housed within the electronic chassis.
Conventional electronic chassis used for high speed switching and networking applications typically are comprised of a metallic box-shaped card cage. Numerous circuit board modules (otherwise known as application cards) are slid into the electronic chassis along card guide assemblies, and are electrically attached to a backplane circuit board located along the backside of the chassis.
Each application card typically includes a large number of electronic components. As a result, these application cards generate a tremendous amount of heat, which must be removed from the chassis to protect the various electronic components within the chassis. As a result, conventional fans have been used to bring cooling air into the chassis, and, at the same time, to exhaust heated air from the chassis.
Various attempts have been made to reduce the temperature with an electronic chassis by providing a fan tray assembly, which includes a plurality of conventional fans. The fan tray assembly may then be housed within the chassis, typically along the top portion of the chassis. Cool air is circulated upward from the bottom of the chassis, through the chassis between the card guide assemblies, and the heated air is exhausted out through the top of the chassis.
Attempts have been made to provide a redundant power scheme to these conventional fans to allow the fans to continue to operate in the event of a power circuitry fail condition. For example, FIG. 2 illustrates one example of a conventional redundant power scheme 100 for a plurality of fans 102, 104. As shown in FIG. 2, power inputs 106, 108 are coupled together via a pair of diodes 110, 112. The combined power inputs 106, 108 are then fed to a single PWM driver 114 for providing fan speed control 115 and a single DC/DC converter 116 for providing voltage to the fans 102, 104. The outputs of the PWM driver 114 and the DC/DC converter 116 are then delivered to all of the fans 102, 104. At the same time, a power bypass-straight input voltage clamp 118 is coupled from the outputs of the diodes 110, 112 directly to the fans 102, 104. The voltage clamp 118 delivers the input voltage directly to the fans 102, 104 in the event that there is a failure of either the PWM driver 114 or the DC/DC converter 116. The input voltage is typically clamped at some specific number since the input power feeds may be as high as 72V.
There are many drawbacks to this conventional redundant power scheme. For example, the redundant power scheme shown in FIG. 2 does not allow for speed control of the fans 102, 104 under fault conditions. That is, when the power bypass clamp 118 is implemented, the fans 102, 104 typically operate at the level of the input voltage. This voltage is typically higher than the maximum operating voltage of the fans 102, 104. As a result, the fans 102, 104 will operate at full speed or greater, which may shorten the life of the fans 102, 104, and may possibly burn out the bearings of the fans or the internal circuitry of the fans. Moreover, operating the fans 102, 104 at an accelerated speed based on the input voltage may create unacceptable and undesirable levels of acoustic noise. As a result, this conventional method of power redundancy is not a desirable option with fans that have lower operating voltages (i.e. 12V or 24V).
FIG. 3 illustrates another example of a conventional redundant power scheme 150 for a plurality of fans 152, 154. As shown in FIG. 3, power input 156 is electrically coupled to a DC/DC converter 158, and power input 160 is electrically connected to a separate DC/DC converter 162. The outputs of the DC/DC converters 158, 160 are coupled together via diodes 164, 166 to provide load sharing, and to provide redundancy in the event that one of the two DC/DC converters 158, 162 fails. In this scenario, the input voltage is applied directly to the fans 152, 154, which minimizes the number of allowable speeds for the fans 152, 154. Moreover, this scenario does not provide full redundancy to allow the fans 152, 154 to operate normally in the event of certain failures. For example, if power input feed 156 shuts down and the DC/DC converter 162 shuts down, then the fans 152, 154 will not receive any power. Similarly, if power input feed 160 shuts down and the DC/DC converter 158 shuts down, then the fans 152, 154 likewise will not receive any power.
Accordingly, it would be desirable to provide an apparatus and method of providing redundant power and redundant fan speed control to a plurality of fans that overcomes the disadvantages described above.
One aspect of the invention provides an apparatus for providing redundant power and redundant fan speed control to a plurality of fans. A first power supply input is electrically connected to a second power supply input to provide a combined power supply input. First and second fan speed controllers each having an input and an output are also provided, along with first and second power converters each having an input and an output. The combined power supply input is electrically connected to the input of the first fan speed controller and to the input of the first power converter. The combined power supply input is also electrically connected to the input of the second fan speed controller and the input of the second power converter. The output of the first fan speed controller is electrically combined with the output of the second fan speed controller to provide a combined fan speed control signal. The combined fan speed control signal is electrically connected to the plurality of fans. The output of the first power converter is electrically combined with the output of the second power converter to provide a combined fan voltage. The combined fan voltage is electrically connected to the plurality of fans. Each of the first and second fan speed controllers may preferably be a PWM driver. The plurality of fans may preferably be comprised of at least to two fans. The at least two fans may preferably be comprised of eight fans. A first diode having an input and an output, and a second diode having an input and an output may also be provided. The input of the first diode may preferably be electrically connected to the first power supply input, and the input of the second diode may preferably be electrically connected to the second power supply input. The output of the first diode may preferably be electrically connected to the output of the second diode. A third diode having an input and an output, and a forth diode having an input and an output may also be provided. The input of the third diode may preferably be electrically connected to the output of the first fan speed controller, and the input of the fourth diode may preferably be electrically connected to the output of the second fan speed controller. The output of the third diode may preferably be electrically connected to the output of the fourth diode. A fifth diode having an input and an output, and a sixth forth diode having an input and,an output may also be provided. The input of the fifth diode may preferably be electrically connected to the output of the first power converter. The input of the sixth diode may preferably be electrically connected to the output of the second power converter. The output of the fifth diode may preferably be electrically connected to the output of the sixth diode. The first power supply input may preferably be comprised of 48V, and the second power supply input may preferably be comprised of 48V. The combined fan speed control signal may preferably be electrically distributed to each of the plurality of fans. Similarly, the combined fan voltage may preferably be electrically distributed to each of the plurality of fans.
Another aspect of the invention provides a method of providing redundant power and redundant fan speed control to a plurality of fans. A first power supply input and a second power supply input are provided. First and second fan speed controllers each having an input and an output may also be provided. Finally, first and second power converters each having an input and an output may also be provided. The first power supply input is electrically connected to the second power supply input to provide a combined power supply input. The combined power supply input is electrically connected to the input of the first fan speed controller and the input of the first power converter. The combined power supply input is electrically connected to the input of the second fan speed controller and the input of the second power converter. The output of the first fan speed controller is electrically combined with the output of the second fan speed controller to provide a combined fan speed control signal. The combined fan speed control signal is electrically connected to the plurality of fans. The output of the first power converter is electrically combined with the output of the second power converter to provide a combined fan voltage. The combined fan voltage is electrically connected to the plurality of fans. Each of the first and second fan speed controllers may preferably be a PWM driver. The plurality of fans may preferably be comprised at least to two fans. The at least two fans may preferably be comprises of eight fans. A first diode having an input and an output, and a second diode having an input and an output may also be provided. The input of the first diode may preferably be electrically connected to the first power supply input. The input of the second diode may preferably be electrically connected to the second power supply input. The output of the first diode may preferably be electrically connected to the output of the second diode. A third diode having an input and an output, and a forth diode having an input and an output may also be provided. The input of the third diode may preferably be electrically connected to the output of the first fan speed controller. The input of the fourth diode may preferably be electrically connected to the output of the second fan speed controller. The output of the third diode may preferably be electrically connected to the output of the fourth diode. A fifth diode having an input and an output, and a sixth forth diode having an input and an output may also be provided. The input of the fifth diode may preferably be electrically connected to the output of the first power converter. The input of the sixth diode may preferably be electrically connected to the output of the second power converter. Finally, the output of the fifth diode may preferably be electrically connected to the output of the sixth diode.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and the equivalents thereof.